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POCan you swap a std::queue with a lambda comparator?
 

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  1. POCan you swap a std::queue with a lambda comparator?
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    <p>I am trying to clear a std::queue using the example in <a href="https://stackoverflow.com/a/709161/837451">https://stackoverflow.com/a/709161/837451</a> via a swap. However, it doesn't seem to work with a lambda comparator due to the "deleted function" error.</p> <p>Minimal <del>working</del> failing example:</p> <pre><code>#include &lt;queue&gt; #include &lt;vector&gt; using namespace std; int main(){ typedef pair&lt;int,float&gt; ifpair; auto comp = []( ifpair a, ifpair b ) { return a.second &gt; b.second; }; typedef priority_queue&lt; ifpair , vector&lt;ifpair&gt;, decltype( comp ) &gt; t_npq; t_npq npq( comp ); //do something with npq. finish using it (without emptying it) and clear for next round t_npq empty( comp ); swap(npq , empty); } </code></pre> <p>Compile with</p> <pre><code>g++ -std=c++11 /tmp/test.cpp -o /tmp/o </code></pre> <p>And I get the following error:</p> <pre><code>/usr/include/c++/4.8/bits/move.h:176:11: error: use of deleted function ‘main()::__lambda0&amp; main()::__lambda0::operator=(const main()::__lambda0&amp;)’ __a = _GLIBCXX_MOVE(__b); ^ /tmp/test.cpp:6:18: note: a lambda closure type has a deleted copy assignment operator </code></pre> <p>g++ -v</p> <pre><code>Using built-in specs. COLLECT_GCC=g++ COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.8/lto-wrapper Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.8.1-10ubuntu9' --with-bugurl=file:///usr/share/doc/gcc-4.8/README.Bugs --enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.8 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.8 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.8-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.8.1 (Ubuntu/Linaro 4.8.1-10ubuntu9) </code></pre> <p>I'm kind of curious what exactly is going on here but more importantly I would really like to know how to make this work.</p>
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    1. COWorks on my machine! What compiler (and version) are you using? Idem for the standard library implementation.
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    2. COSuboptimal quick fix: use `std::function<bool(ifpair,ifpair)>`
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    3. CODo you really want the values to `comp` passed in by value instead of by ref or const ref?
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